You may create a group chat right from IM+. Please tap on "Chat bubbles" button in the upper right corner of contacts window, then select a service the group chat will be created in, select the participants of the group chat and tap on "Done".

IM+ allows you to add contacts into group chat, leave the group chat and set the topic of group chat.
These options are accessible from the chat menu. To access it, please minizmize the keyboard, tap on the arrow
next to the text input field and select the needed action.